The Spemann-Mangold organizer is the structure that provides the signals, which initiate pattern formation in the developing vertebrate embryo, affecting the main body axes. Very little is known about axial induction in the gastrulating human embryo, as research is hindered by obvious ethical restrictions. Human embryonic stem cells (hESCs) are pluripotent cells derived from the pregastrula embryo that can differentiate in culture following a program similar to normal embryonic development but without pattern formation. Here, we show that in hESC-derived embryoid bodies, we can induce differentiation of cells that harbor markers and characteristics of the gastrula-organizer. Moreover, genetic labeling of these cells enabled their purification, and the discovery of a comprehensive set of their secreted proteins, cell surface receptors, and nuclear factors characteristic of the organizer. Remarkably, transplantation of cell populations enriched for the putative human organizer into frog embryos induced a secondary axis. Our research demonstrates that the human organizer can be induced in vitro and paves the way for the study of pattern formation and the initial regulation of body axis establishment in humans.

Human embryonic stem cells differentiate into gastrula organizer cells that express typical markers and induce secondary axes when injected into frog embryos. Here, we report that these human organizer cells express DUXO (DUX of the Organizer), a novel member of the double-homeobox (DUX) family of transcription factors, a group of genes unique to placental mammals. Both of DUXO's homeodomains share high similarity with those of Siamois and Twin, the initial inducers of the amphibian gastrula organizer. DUXO overexpression in human embryoid bodies induces organizer related genes, whereas its knock down hampers formation of the organizer and its derivatives. Finally, we show that DUXO regulates GOOSECOID, the canonical organizer marker, in a direct manner, suggesting that DUXO is a major regulator of human organizer formation.